/**
 *
 *  Base64 encode / decode
 *  文字采用UTF-8方式进行Base64编码
 *
 */

function Base64() {

  // private property
  _keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

  // public method for encoding
  this.encode = function (input) {
    var output=new Array();
    var chr1, chr2, chr3;
    var enc1, enc2, enc3, enc4;
    var i = 0;
    input = _utf8_encode(input);

    while (i < input.length)
    {
      chr1 = input[i++];
      chr2 = input[i++];
      chr3 = input[i++];

      enc1 = chr1 >> 2;
      enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
      enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
      enc4 = chr3 & 63;
      if (isNaN(chr2)) {
        enc3 = enc4 = 64;
      } else if (isNaN(chr3)) {
        enc4 = 64;
      }
      output.push(_keyStr.charAt(enc1) + _keyStr.charAt(enc2) + _keyStr.charAt(enc3) + _keyStr.charAt(enc4));
    }
    return output.join('');
  }

  // public method for decoding
  this.decode = function (input) {
    var output = "";
    var chr1, chr2, chr3;
    var enc1, enc2, enc3, enc4;
    var i = 0;
    input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
    while (i < input.length) {
      enc1 = _keyStr.indexOf(input.charAt(i++));
      enc2 = _keyStr.indexOf(input.charAt(i++));
      enc3 = _keyStr.indexOf(input.charAt(i++));
      enc4 = _keyStr.indexOf(input.charAt(i++));
      chr1 = (enc1 << 2) | (enc2 >> 4);
      chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
      chr3 = ((enc3 & 3) << 6) | enc4;
      output = output + String.fromCharCode(chr1);
      if (enc3 != 64) {
        output = output + String.fromCharCode(chr2);
      }
      if (enc4 != 64) {
        output = output + String.fromCharCode(chr3);
      }
    }
    output = _utf8_decode(output);
    return output;
  }

  // private method for UTF-8 encoding
  _utf8_encode = function (string) {
    string = string.replace(/\r\n/g,"\n");
    var utftext = new Array();
    var utftextlen=0;
    for (var n = 0; n < string.length; n++) {
      var c = string.charCodeAt(n);
      if (c < 128) {
        utftext[utftextlen++] = c;
      } else if((c > 127) && (c < 2048)) {
        utftext[utftextlen++] = (c >> 6) | 192;
        utftext[utftextlen++] = (c & 63) | 128;
      } else {
        utftext[utftextlen++] = (c >> 12) | 224;
        utftext[utftextlen++] = ((c >> 6) & 63) | 128;
        utftext[utftextlen++] = (c & 63) | 128;
      }

    }
    return utftext;
  }

  // private method for UTF-8 decoding
  _utf8_decode = function (utftext) {
    var string = "";
    var i = 0;
    var c = c1 = c2 = 0;
    while ( i < utftext.length ) {
      c = utftext.charCodeAt(i);
      if (c < 128) {
        string += String.fromCharCode(c);
        i++;
      } else if((c > 191) && (c < 224)) {
        c2 = utftext.charCodeAt(i+1);
        string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
        i += 2;
      } else {
        c2 = utftext.charCodeAt(i+1);
        c3 = utftext.charCodeAt(i+2);
        string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
        i += 3;
      }
    }
    return string;
  }

  _exchange_character = function(charArray){
    charArray=charArray.split("");
    for (var i = 0; i < charArray.length; i++)
    {
      // 互换相邻的字符
      if (i > 0 && i % 2 == 0)
      {
        var c = charArray[i];
        charArray[i] = charArray[i - 1];
        charArray[i - 1] = c;
      }
    }
    return charArray.join("");
  }

  //参数需要绕过防火墙可使用此方法加密
  this.encodePostParam = function(input) {
    input=this.encode(input).split("").reverse().join("");
    return _exchange_character(input);
  }

  this.decodePostParam = function(input) {
    input=_exchange_character(input).split("").reverse().join("");
    return this.decode(input);
  }
}
